The goal of the proposed research is to map the distribution of heterogenic and autogenic feedback during locomotion and to determine their underlying mechanisms. To date, the role and distribution of these force-dependent and length-dependent pathways during locomotion remains largely unexplored and controversial. Force responses will be measured in quadriceps muscles and ankle extensors, such as the triceps surae and flexor hallicus longus muscles, during spontaneous locomotion and during the crossed-extension reflex within the same preparation. The goal is to ascertain whether feedback is modulated between the two states. Once the distribution of heterogenic feedback has been mapped among these muscles, autogenic feedback will be analyzed to determine the change in gain during stepping. Experimental methods employed to discern length and force effects include history dependence, vibration, and intramuscular stimulation. Because limitations are associated with each approach, several methods will be completed to determine the contribution of length and force feedback to the change in autogenic gain. This proposed research will not only determine the neural connections between and among these muscles, but also will explore the functional relevance for the feedback pathways from a biomechanical perspective. Determining the contribution of this neural feedback during locomotion is essential for effective rehabilitation of patients with motor deficits, including spinal cord injury. [unreadable] [unreadable]